How to get disconnected teeth and beard to move with rigged face?
I'll try to recreate the similiar issue as yours for you. As you can see below the jaw mesh doesn't follow the head's movement. It's because the jaw's vertices are not properly assigned to the head bone.

Select the head bone in Pose Mode, then select the mesh. In Edit Mode select all the vertices that belongs to jaw. Go to the Mesh Data header and in the Vertex Groups panel assign (press the Assign button) them with the weight of 1.000 to the head bone.


EDIT: I've weight painted the left side of your model. Unfortunatelly it wasn't symmetrical, so I couldn't mirror the weights to the right side of the rig. You'll have to do it manually.
Here's the .blend: